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IAUC 5364: 1991ba; X1850-086; N Sct 1991

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                                                  Circular No. 5364
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

SUPERNOVA 1991ba IN ESO 244-IG32
     M. Della Valle, European Southern Observatory, communicates:
"Preliminary inspection of a low-resolution spectrogram (range 430-
720 nm), obtained on Oct. 9.3 UT with the ESO/Max-Plank-Institute
2.2-m telescope (+ EFOSC2) at La Silla, finds broad H-alpha centered
at 669 nm (FWZI 33 nm), indicating SN 1991ba to be a type-II
supernova. Only a weak H-alpha P-Cyg absorption is visible at 650 nm,
which gives an expansion velocity of about 12 000 km/s (adopting z =
0.024 at the location of the supernova, obtained from a narrow H-
alpha + [N II] emission superimposed on the supernova spectrum).
Other broad absorptions are visible at 451, 482, and 517 nm.  The
slope of the continuum gives B-V about +0.2.  The spectrum therefore
resembles those of other type-II supernovae about 1 week past maximum."

     M. Auriere, Observatoire du Pic du Midi; and L. Koch-Miramond,
C.E.N., Saclay, communicate:  "On 1990 July 29 we obtained CCD
observations, under excellent seeing conditions at the European
Southern Observatory's 3.5-m New Technology Telescope, of the field of
the x-ray source X1850-086 (located in the globular cluster NGC
6712).  From 17 U images of 10-min exposure each (FWHM 0".8-1".0),
and 2 B and 2 V images (FWHM 0".6-0".7), we deduce that star 'S' of
Nieto et al. (1990, A.Ap. 239, 155) is resolved and clearly measured
as an ultraviolet star, for the first time with a homogeneous set of
observations:  B = 21.2 +/- 0.2, U-B = -0.9 +/- 0.3, B-V = +0.2 +/-
0.5.  A dimming of star 'S' by about 0.4 mag (3-sigma) is observed;
this star corresponds to the unresolved ultraviolet object pointed
out by Bailyn et al. (1988, Ap.J. 331, 330) and whose position is
consistent with that of the radio source of Lehto et al. (1990,
Nature 347, 49), and it can thus be considered as the optical counterpart
of the x-ray source.  Object 'Z' of Nieto et al. is not
visible on our images."

     Visual magnitude estimates (cf. IAUC 5348):  Aug. 29.87 UT,
[9.5 (G. Faure, Varces, France); Sept. 27.81, 14.5 (A. Boattini,
Montelupo, Italy); 27.82, 14.5 (M. Tombelli and A. Bartolini,
Montelupo, Italy); Oct. 2.85, 14.7 (A. Boattini and M. Tombelli,
Piazzano, Italy).

1991 October 10                (5364)             Daniel W. E. Green

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